Strength members, reinforcing members, and structural members which are made of metal and have a bent shape are used in automobiles, various types of machines, and the like. These bent members need to have a high strength, a light weight, and a small size. In the past, this type of bent member has been manufactured by methods such as welding of press formed members, punching of thick plates, and forging. However, it is difficult to further reduce the weight and size of bent members manufactured by these methods.
Non-Patent Document 1, for example, discloses the manufacture of this type of bent member by so-called tube hydroforming Page 28 of Non-Patent Document 1 discloses that there are various challenges in the tube hydroforming technique, such as the development of materials for use in the method and increasing the degree of freedom of shapes which can be formed, and that further technological development is necessary.
In Patent Document 1, the present applicant disclosed a bending apparatus. FIG. 13 is an explanatory view schematically showing that bending apparatus 0.
As shown in FIG. 13, the bending apparatus performs the following operations on a steel tube 1 which is a material to be processed and which is supported by a support means 2 so as to be movable in its axial direction while being fed from an upstream side towards a downstream side by a feed device 3 such as a ball screw:
(a) rapidly heating a portion of the steel tube 1 with a high frequency heating coil 5 located downstream of the support means 2 to a temperature range in which quench-hardening is possible,
(b) rapidly cooling the steel tube 1 with a water cooling device 6 disposed downstream of the high frequency heating coil 5, and
(c) imparting a bending moment to the heated portion of the steel tube 1 to perform bending two-dimensionally or three-dimensionally by varying the position of a movable roller die 4 having at least one set of roll pairs 4a which can support the steel tube 1 while feeding it.
As a result, a bent member 8 is manufactured with high operating efficiency while guaranteeing an adequate bending accuracy.